Helical insert for shell and tube heat exchanger

ABSTRACT

A heat transfer tube includes a tube having an internal tube wall, and a tube element extending along a tube length and radially inwardly from the internal tube wall. The tube element has a radial element height less than a hydraulic radius of the tube, and the radial element height is greater than a base element width at the internal tube wall. A tube and shell heat exchanger includes a heat exchanger tube extending through a housing and having a heat transfer medium flowing therethrough. The heat exchanger tube includes a tube having an internal tube wall and tube element extending along a tube length and radially inwardly from the internal tube wall. The tube element has a radial element height less than a hydraulic radius of the tube, and the radial element height is greater than a base element width at the internal tube wall.

BACKGROUND

Exemplary embodiments pertain to the art of heating, ventilation, air conditioning and refrigeration (HVAC&R) systems. More specifically, the present disclosure relates to shell-and-tube heat exchangers for HVAC&R systems.

Shell and tube heat exchangers are utilized in HVAC&R systems, particularly as evaporators in HVAC&R systems, to facilitate a thermal energy exchange refrigerant in the evaporator and a medium, often water, a brine or other solution, flowing through a number of tubes in the evaporator. The thermal energy exchange cools the medium and causes the refrigerant to boil.

BRIEF DESCRIPTION

In one embodiment, a heat transfer tube includes a tube having an internal tube wall, and a tube element extending along a tube length and radially inwardly from the internal tube wall. The tube element has a radial element height less than a hydraulic radius of the tube, and the radial element height is greater than a base element width at the internal tube wall.

Additionally or alternatively, in this or other embodiments the tube element extends helically along the tube length.

Additionally or alternatively, in this or other embodiments the tube element has a ratio of pitch to hydraulic diameter in the range of 1 to 20.

Additionally or alternatively, in this or other embodiments the tube element extends intermittently along the tube length.

Additionally or alternatively, in this or other embodiments the tube element includes a first element portion and a second element portion separate from the first element portion, the first element portion and second element portion overlapping along a lengthwise direction of the tube.

Additionally or alternatively, in this or other embodiments the tube element is configured to extend through a thermal boundary layer of a heat transfer medium flowing therethrough.

Additionally or alternatively, in this or other embodiments the tube element is a helical feature formed integral to the tube.

Additionally or alternatively, in this or other embodiments a single, unitary tube element extends radially inwardly from the internal tube wall at a cross-section perpendicular to the tube length.

Additionally or alternatively, in this or other embodiments the tube is formed from a first material, and the tube element is formed from a second material different from the first material.

Additionally or alternatively, in this or other embodiments the heat transfer tube includes one or more surface enhancements including one or more of axial, helical or crosshatched microfins or reentrant cavities.

In another embodiment, a tube and shell heat exchanger includes a housing and a heat exchanger tube extending through the housing and having a heat transfer medium flowing therethrough. The heat exchanger tube includes a tube having an internal tube wall and tube element extending along a tube length and radially inwardly from the internal tube wall. The tube element has a radial element height less than a hydraulic radius of the tube, and the radial element height is greater than a base element width at the internal tube wall. The heat exchanger includes a refrigerant inlet to flow a refrigerant over the heat exchanger tube, for thermal energy exchange between the refrigerant and the heat transfer medium.

Additionally or alternatively, in this or other embodiments the tube element extends helically along the tube length.

Additionally or alternatively, in this or other embodiments the tube element has a ratio of pitch to hydraulic diameter in the range of 1 to 20.

Additionally or alternatively, in this or other embodiments the tube element extends intermittently along the tube length.

Additionally or alternatively, in this or other embodiments the tube element includes a first element portion and a second element portion separate from the first element portion, the first element portion and second element portion overlapping along a lengthwise direction of the tube.

Additionally or alternatively, in this or other embodiments the tube element is configured to extend through a thermal boundary layer of a heat transfer medium flowing therethrough.

Additionally or alternatively, in this or other embodiments the tube element is a helical feature formed integral to the tube.

Additionally or alternatively, in this or other embodiments a single, unitary tube element extends radially inwardly from the internal tube wall at a cross-section perpendicular to the tube length.

Additionally or alternatively, in this or other embodiments the tube is formed from a first material, and the tube element is formed from a second material different from the first material.

Additionally or alternatively, in this or other embodiments, the heat exchanger tube includes one or more surface enhancements including one or more of axial, helical or crosshatched microfins or reentrant cavities.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 is a schematic view of a heating, ventilation, air conditioning and refrigeration (HVAC&R) system;

FIG. 2 is a cross-sectional view of an embodiment of an evaporator for an HVAC&R system;

FIG. 3 is a cross-sectional view of an embodiment of a tube for a heat exchanger;

FIG. 4 is perspective view of an embodiment of a tube for a heat exchanger of an HVAC&R system;

FIG. 5 is a cross-sectional view of another embodiment of a tube for a heat exchanger of an HVAC&R system; and

FIG. 6 is a perspective view of yet another embodiment of a tube for a heat exchanger of an HVAC&R system.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

A typical tube of a shell and tube heat exchanger may have features or “enhancements” to improve thermal energy transfer between the medium and the refrigerant. One such enhancement is a twisted tape inset that extends entirely across an inner diameter of the tube. These inserts however typically result in a high pressure drop penalty along a length of the tube.

Shown in FIG. 1 is a schematic view an embodiment of a heating, ventilation, air conditioning and refrigeration (HVAC&R) system 10, for example, a chiller. A flow of vapor refrigerant 14 is directed into a compressor 16 and then to a condenser 18 that outputs a flow of liquid refrigerant 20 to an expansion valve 22. The expansion valve 22 outputs a vapor and liquid refrigerant mixture 24 to an evaporator 12. A thermal energy exchange occurs between a flow of heat transfer medium 28 flowing through a plurality of evaporator tubes 26 into and out of the evaporator 12 and the vapor and liquid refrigerant mixture 24. As the vapor and liquid refrigerant mixture 24 is boiled off in the evaporator 12, the vapor refrigerant 14 is directed to the compressor 16.

Referring now to FIG. 2, in some embodiments, the evaporator 12 is a falling film evaporator. While a falling film evaporator 12 is shown in FIG. 2 and described herein, one skilled in the art will readily appreciate that the present disclosure may be readily applied to other shell-and-tube heat exchangers, such as a flooded evaporator or a condenser.

The evaporator 12 includes housing 52 with the evaporator 12 components disposed at least partially therein, including a separator 30 to separate liquid refrigerant 20 and vapor refrigerant 14 from the vapor and liquid refrigerant mixture 24. Vapor refrigerant 14 is routed from the separator 30 through a suction port 32 and toward the compressor 16, while the liquid refrigerant 20 is routed toward a distribution system 34 of the evaporator 12. The distribution system 34 includes a distribution box 36 having a plurality of openings 38 arrayed along a bottom surface 44 of the distribution box 36. Though in the embodiment of FIG. 2 the distribution box 36 is substantially rectangular in cross-section, it is to be appreciated that the distribution box 36 may have another cross-sectional shape, for example, T-shaped or oval shaped. The distribution box 36 and openings 38 are configured to drip liquid refrigerant 20 onto evaporator tubes 26 and resulting in the falling film terminating in a refrigerant pool 40 at a bottom of the evaporator 12. A feed pipe 42 extends from the separator 30 into the distribution box 36 and terminates in the distribution box 36. Flow of the liquid refrigerant 20 into the distribution box 36 results in the collection of a volume of liquid refrigerant 20, or liquid head 46, in the distribution box 36 prior to flowing through the drip openings 38. In some embodiments, a vent 56 may be located at the distribution system 34, for example, at the distribution box 36 to allow escape of vapor refrigerant 14 that makes its way into the distribution system 34 from the separator 30 thereby preventing an unwanted buildup of vapor refrigerant 14 in the distribution system 34.

Heat transfer medium 28 flows through the evaporator tubes 26 for thermal energy exchange with the liquid refrigerant 20. Referring now to FIG. 3, the tube 26 typically has a circular cross-section, with a central axis 60. In some embodiments, the evaporator tube 28 has internal or external enhancements including one or more of axial, helical or crosshatched microfins or reentrant cavities. The heat transfer medium 28 is a single-phase liquid, and in some embodiments is a high Prandtl number fluid such as a low-temperature brine or glycol. In some embodiments, the fluid has a Prandtl number in the range of 7 to 200. In such fluids, a thermal boundary layer 64 is a much thinner layer than a fluid momentum boundary layer. In other words, the fluid momentum boundary layer edge is located radially further inboard from a tube inner wall 62 than is the thermal boundary layer 64. Heat transfer is improved while minimizing the pressure drop increase by mixing the thermal boundary layer 64 with a core flow 66 located radially inboard of the thermal boundary layer 64, while minimizing the disturbance of the core flow 66.

Referring now to FIG. 4, to provide the mixing of the thermal boundary layer 64 and the core flow 66, a tube element, such as a helical insert 68, is located inside the evaporator tube 26 and extends along a length of the evaporator tube 26. As shown best in FIG. 3, the insert 68 is rectangular in cross-section, with an insert height 70 radially inboard from the tube inner wall 62 greater than a circumferential insert width 72. In some embodiments, an aspect ratio of insert height 70 to insert width 72 is in the range of 1 to 200.

In an alternative embodiment, as shown in FIG. 5, the insert 68 may have a circular cross-section with an insert diameter 74. In still other embodiments, the insert may have other cross-sectional shapes, such as oval or elliptical or other curvilinear shapes, or triangular or other polygonal shapes.

Referring again to FIG. 3, the insert height 70 is less than a tube hydraulic radius, and in some embodiments may be expressed as:

-   -   Height=C*sqrt(L/D)*(D/((P_(r) ^(1/3))*sqrt(Re_(D)))     -   Where: L=tube length;         -   D=tube hydraulic diameter;         -   Pr=Prandtl number of the heat transfer medium 28;         -   Re_(D)=Reynolds number at the tube effective diameter; and     -   C=a constant having, in some embodiments, a value between 2         and 5. In other embodiments, the constant C has a value between         2.5 and 3.5.

In embodiments with circular inserts 68, insert diameter 74 is substituted for insert height 70. The insert height 70 is established to extend through the thermal boundary layer 64, while causing minimal disturbance to the core flow 66.

Referring again to FIG. 4, in some embodiments, the helical insert 68 extends helically along the tube length and has an insert pitch 76, or a distance over the tube length at which the insert 68 traverses a full 360 degree rotation about the tube 26. To have a greater mixing effect and thus a greater influence on thermal energy transfer, a narrower insert pitch 76 is selected, while to have a lesser effect on thermal energy transfer, a wider or longer insert pitch 76. In some embodiments, a ratio of insert pitch 76 to tube maximum internal diameter D is in the range of 1 to 20.

In some embodiments, such as shown in FIG. 4, a single helical insert 68 is utilized, such that a single protrusion or insert height 70 is present at a cross-section taken perpendicular to the tube length. While a single helical insert 68 is shown in the present drawings and described herein, one skilled in the art will readily appreciate that a double-helical insert may be utilized in some embodiments. Further, one skilled in the art will readily appreciate that the present disclosure may be readily applied to evaporator tubes 26 having cross-sectional shapes other than circular, such as evaporator tubes 26 having oval, elliptical, rectangular or square cross-sections.

Referring now to FIG. 6, in some embodiments the helical insert 68 may extend intermittently along the tube length 76, and may be defined by a plurality of insert segments 80. In some embodiments, the insert segments 80 extend in a helical direction along the tube length, while in other embodiments the insert segments 80 each extend parallel to the tube length 76. In some embodiments, insert segments 80 may overlap along the tube length 76.

While in some embodiments, the helical insert 68 is secured to the tube inner wall 62, such intimate contact along an entire length of the helical insert 68 is not necessary, as the primary purpose of the helical insert 68 is to provide flow mixing of the heat transfer medium 28 to enhance heat transfer through the heat transfer medium 28.

The helical insert 68 may be formed from the same material as the evaporator tube 26, such as aluminum or copper or alloys thereof, and further may be formed integral with the evaporator tube 26. In other embodiments, the helical insert 68 is formed separately from the evaporator tube 26, and is installed via a secondary operation. Further, the helical insert 68 may be formed from a material different from the material utilized to form the evaporator tube 26, such as a metal or polymer material.

The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.

While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims. 

What is claimed is:
 1. A heat transfer tube comprising: a tube having an internal tube wall; and a tube element extending along a tube length and radially inwardly from the internal tube wall, the tube element having a radial element height less than a hydraulic radius of the tube, and the radial element height is greater than a base element width at the internal tube wall.
 2. The heat transfer tube of claim 1, wherein the tube element extends helically along the tube length.
 3. The heat transfer tube of claim 2, wherein the tube element has a ratio of pitch to hydraulic diameter in the range of 1 to
 20. 4. The heat transfer tube of claim 1, wherein the tube element extends intermittently along the tube length.
 5. The heat transfer tube of claim 4, wherein the tube element includes a first element portion and a second element portion separate from the first element portion, the first element portion and second element portion overlapping along a lengthwise direction of the tube.
 6. The heat transfer tube of claim 1, wherein the tube element is configured to extend through a thermal boundary layer of a heat transfer medium flowing therethrough.
 7. The heat transfer tube of claim 1, wherein the tube element is a helical feature formed integral to the tube.
 8. The heat transfer tube of claim 1, further comprising a single, unitary tube element extending radially inwardly from the internal tube wall at a cross-section perpendicular to the tube length.
 9. The heat transfer tube of claim 1, wherein the tube is formed from a first material, and the tube element is formed from a second material different from the first material.
 10. The heat transfer tube of claim 1, further comprising one or more surface enhancements including one or more of axial, helical or crosshatched microfins or reentrant cavities.
 11. A tube and shell heat exchanger, comprising: a housing: a heat exchanger tube extending through the housing and having a heat transfer medium flowing therethrough, the heat exchanger tube including: a tube having an internal tube wall; and tube element extending along a tube length and radially inwardly from the internal tube wall, the tube element having a radial element height less than a hydraulic radius of the tube, and the radial element height is greater than a base element width at the internal tube wall; and a refrigerant inlet to flow a refrigerant over the heat exchanger tube, for thermal energy exchange between the refrigerant and the heat transfer medium.
 12. The tube and shell heat exchanger of claim 11, wherein the tube element extends helically along the tube length.
 13. The tube and shell heat exchanger of claim 12, wherein the tube element has a ratio of pitch to hydraulic diameter in the range of 1 to
 20. 14. The tube and shell heat exchanger of claim 11, wherein the tube element extends intermittently along the tube length.
 15. The tube and shell heat exchanger of claim 14, wherein the tube element includes a first element portion and a second element portion separate from the first element portion, the first element portion and second element portion overlapping along a lengthwise direction of the tube.
 16. The tube and shell heat exchanger of claim 11, wherein the tube element is configured to extend through a thermal boundary layer of a heat transfer medium flowing therethrough.
 17. The tube and shell heat exchanger of claim 11, wherein the tube element is a helical feature formed integral to the tube.
 18. The tube and shell heat exchanger of claim 11, further comprising a single, unitary tube element extending radially inwardly from the internal tube wall at a cross-section perpendicular to the tube length.
 19. The tube and shell heat exchanger of claim 11, wherein the tube is formed from a first material, and the tube element is formed from a second material different from the first material.
 20. The tube and shell heat exchanger of claim 11, further comprising one or more surface enhancements including one or more of axial, helical or crosshatched microfins or reentrant cavities. 